Obesity Dr. Sumbul Fatma

Obesity A disorder of body weight regulatory systems Causes accumulation of excess body fat >20% of normal body weight Obesity is associated with a high risk of: Diabetes mellitus Hypercholesterolemia High plasma triglycerides Hypertension Heart disease Cancer Gallstones, arthritis, gout Mortality

Body Mass Index (BMI) BMI is an indirect measure of obesity Correlates height, weight and amount of body fat in an individual High BMI is associated with increased mortality risk BMI GRADE UNDER WEIGHT ≤ 18.5 NORMAL 18.5 – 24.9 OVER WEIGHT 25.0 – 29.9 OBESE 30.0 – 34.9 I 35.0 – 39.9 II HIGHLY OBESE ≥ 40 III

Anatomic differences in fat deposition Health risks depend on the pattern of fat deposition Android, “apple-shaped,” or upper body obesity excess body fat deposited in the central abdominal area Associated with risk of hypertension, insulin resistance, diabetes, dyslipidemia, and coronary heart disease

Anatomic differences in fat deposition Gynoid, “pear-shaped,” or lower body obesity Fat deposited around the hips or gluteal region. Associated risks are lower

Biochemical differences in fat deposits Abdominal fat Gluteal Fat Smaller cells Larger cells More responsive to hormones Less responsive Release substances via portal vein to the liver Release substances to circulation with no effect on the liver

Adipocytes Triacylglycerols are deposited in adipocytes (fat cells) The cells increase in size and expand and divide Fat cells, once gained, are never lost In obesity adipocytes increase in number and size Reduction in weight causes adipocytes to reduce in size

Factors contributing to obesity Genetic: familial tendency Environmental and behavioral Sex: women more susceptible Activity: lack of physical activity Psychogenic: emotional deprivation/depression Alcohol: problem drinking Smoking: cessation smoking Drugs: e.g. tricyclic derivatives

Causes of weight Gain Energy imbalance Over a long period of time calories consumed not equal to calories used Over a long period of time Due to a combination of several factors Individual behaviors Social interactions Environmental factors Genetics

More in and less out = weight gain More out and less in = weight loss Hypothalamus control center for hunger and satiety Endocrine disorder where are the hormones?

Hormonal control Appetite is influenced by afferent neural signals, circulating hormones, and metabolites These signals cause the release of hypothalamic peptides and activate efferent neural signals Adipocytes also function as endocrine cells They release many regulatory molecules: Leptin, adiponectin, resistin Low levels of adiponectin and increased levels of resistin, may cause insulin resistance observed in obesity

Leptin A protein hormone produced by adipocytes Required to keep the body weight under control Signals the brain about fat store level Regulates the amount of body fat by: Controlling appetite and energy expenditure Leptin secretion: Suppressed in starvation (depletion of fat stores) Enhanced in well-fed state (expansion of fat stores) Leptin causes overweight mice to lose weight and maintain weight loss

Leptin Resistance Leptin increases metabolic rate and decreases appetite in humans Plasma leptin level in obese humans is usually normal for their fat mass Resistance to leptin has been found in obese humans The receptor for leptin in the hypothalamus is produced db gene Mutation in db gene causes leptin resistance in mice Leptin resistance may have some role in human obesity Dieting decreases leptin levels Reducing metabolism, stimulating appetite

Adiponectin Exclusively and abundantly secreted hormone from the adipocytes Promotes the uptake and oxidation of fatty acids and glucose by muscle and liver Blocks the synthesis of fattyacids and gluconeogenesis by hepatocytes Net effect is to increase the sensitivity to insulin, and improve glucose tolerance

Adiponectin Adiponectin levels are inversely correlated with body fat percentage and parallels with the HDL level Low levels are seen in metabolic syndrome and diabetes mellitus

Other Hormones Ghrelin: A peptide hormone secreted by stomach Stimulates appetite Secretion increases just before meals and drops after meals Increases food intake Decreases energy expenditure and fat catabolism Levels in dieters are higher after weight loss The body steps up ghrelin production in response to weight loss The higher the weight loss, the higher the ghrelin levels

Other Hormones Cholecystokinin: Peptides released from the gut after a meal satiety signals to the brain Insulin: Promotes metabolism

Metabolic Changes in Obesity Adipocytes send signals that cause abnormal metabolic changes such as: Dyslipidemias Glucose intolerance Insulin resistance

Weight loss Decreases risk factors Leads to: Lower blood pressure Decreased serum triacylglycerols Lower blood glucose levels Increase in HDL levels Decreased mortality Beneficial changes in BMR Decreased energy requirement Slow weight loss is more stable

Treatment options Physical activity combined with healthy diet decreases level of obesity Reduces risk for heart disease and diabetes Dieting Use of calorie-restricted diet Restriction of energy intake

Drugs Sibutramine An appetite suppressant Inhibits the reuptake of both serotonin and norepinephrine Orlistat A pancreatic and gastric lipase inhibitor Decreases the breakdown of dietary fat

Surgery Surgical procedures are designed to reduce food consumption in patients with BMI >40 Used when other treatment options fail

Reference Lippincott’s Illustrated Reviews of Biochemistry 4th Edition

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